1. Field of the Invention
Embodiments of the invention relate to a conductor loop, which is completely embedded in an article. The article includes a base body of a polymer material with elastic properties. The two relevant polymer material groups are elastomers or thermoplastic elastomers. Usually, the article is additionally provided with a strengthening support, in particular, embedded completely in the elastic base body. The conductor loop is used in particular for a conveyor belt.
2. Discussion of Background Information
With regard to conductor loop technology, reference is made in particular to the following patent literature: DE 40 14 475 A1; DE 44 44 264 C1; DE 196 07 867 A1; DE 198 27 120 A1; DE 198 31 854 A1; DE 101 00 249 A1; EP 0 213 057 A1; EP 1 097 094 B1; WO 2005/030621 A1; AU 57 558 B; GB 1 246 786 A; and U.S. Pat. No. 4,621,727, the disclosures of which are expressly incorporated by reference herein in their entireties.
Conveyor belt conductor loop technology is discussed in more detail below.
It is usual to provide conveyor belts with conductor loops in order to detect the occurrence of longitudinal rips. These conductor loops are checked for intactness with the aid of a transmitter/receiver combination. If a longitudinal rip occurs in the conveyor belt, the conductor loop is also destroyed and the transmitter/receiver transmission path is interrupted. This provides a criterion for stopping a conveyor belt at the beginning of the ripping process and limiting the length of the rip. The maximum possible length of the rip is thereby restricted to the distance between two conductor loops. Unfortunately, after the conveyor belts have been in use for some time, false alarms occur with increasing frequency, caused by the conductor loop being destroyed without a rip occurring in the belt.
The conductor loops often includes metal cords, in particular steel cords, incorporated in a meandering form. The cords usually include in turn of at least five stranded wires or flexes. A cord structure of the type 7×7 is preferred for this, with a single wire diameter of approximately 0.2 mm and a total diameter of 1.5 mm to 2 mm. There are also variants including a mixed structure of copper stranded wires and steel stranded wires, particularly with the steel stranded wires enclosing the copper stranded wires. A version including a solid copper wire enclosed by steel stranded wires is also known.
The meandering structure (DE 196 07 867 A1, FIG. 1) is particularly suitable for increasing the extensibility of the loops, since they would otherwise be destroyed after a relatively short time by the mechanical stressing in the conveyor belt, to be specific flexural stress and applied stress. Producing the meander requires the use of a relatively ductile material, which however has adverse effects on the lifetime of the conductor loop. Although materials with higher elasticity improve the fatigue strength of the individual cord, they make it more difficult to form this meander. The use of so-called “high elongation” cords (HE cords), which are able to extend more than the cords as a result of their structure, also improves the lifetime, but likewise makes it more difficult to form the meanders.
The laid-open patent application DE 101 00 249 A1 presents a conductor loop which has a higher cord mass within the peripheral region of the conveyor belt than in the central region of the conveyor belt. At the same time, the conductor loop is also free from crossing points. With such a structural design, it is possible to achieve a higher electromagnetic sensitivity.
The laid-open patent application WO 2005/030621 A1 concerns a recent conductor loop development. For the purpose of providing a highly flexible and highly extensible conductor loop with an increased lifetime, it proposes forming the conductor loop as an open flex helix, wherein each individual wire is enclosed by a polymer material with elastic properties. This measure also prevents internal friction between the wires.
The drawbacks of conductor loops of the prior art specified here, according to which the conductor loop cords usually include steel, is their susceptibility to corrosion, their low flexibility, in spite of the measures according to WO 2005/030621 A1, their low extensibility and, finally, the fallible connection within the endless closure.